$79 Cheap Southwest Airlines flights St. Louis (STL) to Denver (DEN)

Landing cheap one-way Southwest Airlines flights from STL to DEN from $79 on Expedia is a breeze --- just filter by "Price (lowest to highest)." Or check out our affordable round-trip fares from $157 for your next adventure.**These prices were available on Expedia within the past 7 days, for flights departing within the next year. Prices and availability are subject to change. Additional terms apply.

Look for cheap Southwest Airlines flights from Lambert-St. Louis Intl. Airport (STL) to Denver Intl. Airport (DEN) one to three months ahead of your departure. Travelers who book domestic flights 34 to 86 days in advance can save 25% compared to those who book just 6 to 12 days ahead. Regardless of fare type and itinerary, the best day to book a domestic flight is generally Sunday and the most expensive day is typically Monday. Passengers who book on a Sunday can save 6% on average compared to those who book on a Monday.**Ideal booking window recommendation is based on average round-trip ticket prices for January through November for 2024. Best day of the week to book recommendation is based on average round-trip ticket prices for January through October 2024. All data sourced from ARC's global airline sales database.

The first flight from STL to DEN with Southwest Airlines leaves at 6:25AM UTC-6. You'll land at 8:00AM UTC-7. The last Southwest Airlines flight of the day takes off at 8:35PM UTC-6 and arrives at 10:05PM UTC-7. With around 20% fewer cancellations for morning departures, heading out early is usually the wisest option.**Most reliable time of the day recommendation is based on January through August 2024 flight status data sourced from OAG's global flight data platform.